The proposed research is to examine confounding factors that may alter the response of animals to microwave exposure. Quantitative relations among power density (specific absorption rate), body temperature, physiologic regulation and tissue injuries have been derived. In descending order of severity they are: acute tissue injuries (increased serum enzymes, 41.5 C colonic temperature for 30 min.); "stressful" microwave exposure (increased corticosterone, decreased thyrotropin, decreased growth hormone, increased weight loss during exposure, inhibited growth rate, decreased baseline colonic temperature, decreased feed consumption, decreased urine output, decreased urinary corticosterone output and decreased fecal discharge, 40 mW/cm2, 39.6 C colonic temperature); physiological endocrine response (decreased thyrotropin and increased colonic temperature only, 10 mW/cm2, 37.6 C); and subtle physiologic adjustment (inhibited circadian elevation of corticosterone, less than 10 mW/cm2 without increment in body temperature). It is proposed to study interactions of the physiologic status of animals on microwave biological responses: increased metabolic rate relative to resting or inactivity (reversed day-light cycle); limited heat dissipation (tail docking, desalivation); facilitated heat dissipation (hair clipping); durg-induced hypothermia (deprivation of energy substrate and loss of neural control on body temperature); and genetic hypersensitivity to stressors. In addition, the influence of environmental condition will be evaluated. The purpose of these studies is to evaluate the mechanisms and nature of reactions based on a severity scale of bioeffects as described. This study can also serve to test the robustness of microwave bioeffects to exposure intensity (specific effect) and to body temperature (non-specific effect). Furthermore, fast reacting hormones (corticotropin, epinephrine and norepinephrine) will be studied in rats with an indwelling atrial cannula and radio-telemeter to further characterize the physiologic adjustments of animals to microwave fields.